Recovery of the heart after normothermic ischemia. Part II: Myocardial function during postischemic reperfusion.

Contraction and relaxation of the canine myocardium were examined during normothermic ischemia in an isolated heart model. Decrease in the development of tension depends on the duration of ischemia. Deficient functional recovery was observed after ischemic periods extending beyond 30 minutes, in spite of reperfusion periods of over 1 hour. A decrease in compliance was observed during the anoxic period, but a persistent defect of relaxation occurred only after 60 minutes of ischemia. After this period there was also a disturbance in the autoregulative mechanisms of coronary perfusion and an uncoupling of O2-consumption and mechanical efficiency. A prolonged reperfusion period of the heart beating empty allowed ultrastructural recovery of the damaged myocardium. In contrast, functional recovery of the myocardium, as determined by several parameters of contraction and relaxation, did not correlate with ultrastructural recovery and was not improved by prolonged reperfusion.